Nanometer (nm) is a unit of length; one nanometer is equal to one billionth of a meter (10−9 m), which is approximately the size of a DNA molecule or one ten-thousandth of the width of human hair. The term “nano-scale” refers to a size of approximately 1 nm to 100 nm, which falls between the size of a molecule and submicron-scale. A “nanoparticle”, i.e., a nano-scale particle is so small that classic theories are no longer applicable, while quantum effect becomes non-negligible. Since nano-scale materials have a large surface-to-volume ratio, high density in accumulation, and high flexibility in structure formation, the physical and chemical properties of a nano-scale material are significantly different from the properties of the same material in macro-scales. For example, the color of gold nanoparticles are red, not gold. Such phenomenon shows that the optical properties vary when the size of a material is in nanometer scale. As another example, the texture of graphite is soft and thus it can be used for making pencil leads, but the strength of carbon nanotubes made of a carbon nano material is much stronger than the strength of stainless steel, and also providing a very good flexibility.
With the foregoing reasons, more and more studies have been spent on nanotechnology, resulting in developments in many areas from consumer's products to high-tech industries. Particularly, it is a trend to study how precious metal materials such as gold and silver may be applied to daily necessities by nanotechnology. For example, nano-scale gold is used to make clothes and catalytic materials; due to its capability of carrying oxygen, it promotes human blood circulations and metabolism and also activates cells. As another example, silver is non-toxic, and it has an anti-bacteria effect that can kill more than 600 types of germs (general antibiotics can kill only 6 types of germs). Furthermore, silver nanoparticles are even more active than macro-scale silver. Therefore, applying silver nanoparticles in anti-bacteria, deodorant and antiseptic applications may provide great effects.
More specifically, silver nano-scale particles and silver ions released from nano-scale silver have a significant anti-bacteria effect that they are capable of suppressing over 99% of the colon bacillus, staphylococcus aureaus, salmonellosis, and pseudomonas aeruginosa, etc., due to the biological effect of silver as follows. The active silver ions released from nano-scale silver can quickly absorb and combine with the sulfur-hydrogen radicals of the proteases in germs, such that the enzyme of the sulfur-hydrogen radicals becomes inactive and causes the death of germs. Silver nanoparticles carrying positive electric charges and microorganism cells carrying negative charges will attract each other so that the silver nanoparticles will puncture through the outer cell wall to change the internal properties and reduce the growing ability of the microorganism, so that the cells cannot continue their metabolism or reproduction until they die. It is noteworthy that after the death of the germs, silver ions will shift from the dead germs to live germs, and the same action will be repeated until all the germs are eliminated. Therefore, nano-scale silver as an anti-bacteria material has many advantages, including long active lifetime, non-toxic, that it does not result in drug resistance or allergic reaction, that it does not require any light for its activation, and that it is not affected by pH values. Nano-scale silver can also be used for suppressing the growth of moulds for antiseptic function.
In view of the foregoing facts, in recent years many manufacturers for containers made of a porous material (such as stone pots, stone kettles, ceramic pots and ceramic kettles) attempt to apply nano-scale precious metal material to the manufacture of such containers, so as to provide, for example, anti-bacteria, antiseptic, and deodorant effects, and catalyzing effects to improve food smell and taste. The conventional method to do so is to mix the precious metal nanoparticles with a diluted adhesive solution, and then immerse the container made of a porous material into the solution. Next, the container is removed from the solution and dried to produce a container coated with precious metal nanoparticles. However, in the container produced by such a conventional method, due to surface tension of the solution, the precious metal nanoparticles do not permeate into the pores densely distributed on the surface of the container but are only loosely attached onto the surface of the container. Thus, after the container is dried, there is only a thin film of precious metal nanoparticles formed on the surface of the container, which may easily be worn out or peeled off when, for example, washed for several times, and the anti-bacteria, antiseptic, deodorant and catalytic effects will be lost. Therefore, it is desired in this art to manufacture a container made of a porous material wherein precious metal nanoparticles permeate into the pores densely distributed on the surface of the container and sintered therewith, so as to form a robust precious metal nanoparticles film that is not easily worn out nor peeled off.